Step 1: First-Materials and Tools

Step 2: Second-Marking

First place our tounge depressor on the back of the sandpaper, then with help of a pencil mark the outline of the depressor.

Step 3: Third-Gluing

Now put some glue on the area you marked on the sandpaper and scatter with the same tongue depressor (or finger), then put the tongue depressor on paper with glue and push to get for the excess glue out.

Step 4: Fourth-Clamping

To make things easier and to better fit our work we will help with the use of clamps to press, to put it another tongue depressor on the opposite side of the sandpaper an then put our clamps, and leave it for about 20 or 30 minutes and can remove the clamps.

Step 5: Fifth-Cutting and Finishing

Now with the help of a scissors or cutter cut the excess sandpaper, use the line marked above.

Simple yet very good. As you seem to have pictured nail-files / boards you should add some tags to that effect (women look here too). Did you use emery paper? (I believe it's corundum rather than quartz.)

thanks lemoine, i use automotive sandpaper (work on wet or dry), which is widely used for sanding automotive paints, lacquer, varnish, etc. But you can use any kind of sand or emery paper, depends the use you want